A variety of devices for blood separation, including centrifugal devices, are known. Some blood separation devices are limited to a discontinuous process in which a bowl-shaped chamber is filled and then emptied. An example is the Latham bowl, which includes a cone shaped centrifuging chamber with inlet and outlet channels that are part of a stationary element coupled to the rotating chamber via a low friction rotary seal whose function, besides sealing, is to preserve blood sterility during operation. Once inside the device, blood, due to centrifugal force, separates into components in the space between the external and the internal bowl. The lighter component (the supernatant, i.e., plasma with various impurities coming from the surgical field, platelets and white cells, collects towards the inner side of the chamber while the heavier blood components, i.e. the red blood cells, accumulate and concentrate towards the bowl outer diameter. Once the bowl is almost completely filled with red cells, blood flow is stopped. Saline is forced through the red cells and washes them by removing the impurities. After a certain amount of saline has passed through the bowl, the washing step is finished and the centrifugation is stopped. The red cells are then removed from the bowl and made available for reinfusion to the patient. The bowl is now ready to start a new cycle.
An existing device that allows continuous flow separation of salvaged blood is the Fresenius C.A.T.S., but it uses a non-axial symmetric chamber, having the shape of a tubular channel with variable radius. The Fresenius C.A.T.S. is a rather complex unit that does not provide a performance that is superior to that provided by the Latham bowl.
Another continuous flow device, the Biofluid bowl, is described in WO 2007/098623. The Biofluid bowl is equipped with a red blood cell collector and a supernatant collector. Blood entering the bowl hits the bottom of the bowl and, due to centrifugation, is pushed out forming a thin layer on the inner surface of the bowl in which the blood separates into red blood cells on the outside of the thin layer and supernatant on the inside of the thin layer. As the two layers reach the red blood cell collector and the supernatant collector, each layer can be separately collected. A continuous saline flow injected into the bowl through an expressly provided inlet removes impurities from the red blood cell layer.